BIOL-2026EL Study Guide - Final Guide: Saccharomyces Cerevisiae, Staphylococcus Epidermidis, Congo Red
1 Feb 2021
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Document Summary
The negative staining technique allows the observer to see unstained bacteria and other microorganisms on a coloured background, and to determine their morphology. Acid dyes such as congo red and nigrosin are used. These dyes have a negative charge and are repelled by the negatively-charged cytoplasm of bacteria. Thus, the cells are not deformed during the procedure. Under the microscope, bacterial cells will appear clear agains a dark background. Care must be taken to ensure that an excessive amount of dye is not used or it will be more difficult to locate the bacteria. Also, the dye should not become contaminated because it will support bacterial growth. A contaminated dye will not provide the appropriate results. The negative stain technique can be used for samples from bacterial cultures, and especially for microorganisms that are found in dental plaque. Spirochetes in dental plaque do not stain well with simple stains.
